Relieving pressure vessels when subjected to high temperatures



Aug. 14, 1951 G. R. BENZ ETAL 2,564,295

RELIEVING PRESSURE vEsSELs WHEN SUBJECTED TO HIGH TEMPERATURES 7 Filed July 30, 1946 2 Sheets-Sheet l FIG.|. IE]

IN V EN TORS J/Q MANN (MAW ATTORNEYS Aug. 14, 1951 G. R. BENZ ET AL RELIEVING PRESSURE VESSELS WHEN v SUBJECTED TO HIGH TEMPERATURES 2 Sheets-Sheet 2 Filed July 30, 1946- !NVENTOM Q. BY 0. M

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A TTORNEYS Ear-exited Aug. 14, 1951 RELIEVING PRESSURE VESSELS WHEN SUB- JECTED TO HIGH TEMPERATURES George B. Benz and Elmer O. Mattocks, Bartlesville, kla., assignors to Phillips Petroleum Company, a corporation of Delaware Application July 30, 1946, Serial No. 687,130

13 Claims. 1 The invention relates to safety devices and more particularly to devices for relieving pressure vessels when subjected to high temperature.

arrangement like that of Fig. 2, but having each bimetallic thermostat replaced by a thermocou-'- ple-millivoltmeter combination in which the circuits are closed by means of a sliding contact at- In the storing of liquefied petroleum gas such 5 tached to the pointer of the millivoltmeter. .as propane, it is the custom to provide pressure In the following description and in the claims, relief valves to prevent building up unsafe presvarious details will be identified by specific names sures. Practice has shown that these relief valves for convenience, but they are intended to be as are not adequate when high pressures are caused generic in their application as the art will perby fire since the fire often weakens the tank mit. structure with the result that the tank ruptures Like reference characters denote like parts in at a pressure equal to or less than that at which the several figures of the drawings. the pressure relief valves are set. In the drawings accompanying and forming An object of the invention is to provide a part of this specification, certain specific distemperature responsive safety device capable of i5 closure of the invention is made for purposes of use with the normal pressure operated relief explanation, but it will be understood that the valve or separately therefrom, details may be modified in various respects with- According to a preferred form of the invenout departure from the broad aspect of the intion, a plurality of thermocouples are provided vention. whose hot junctions are distributed around the R r i w to the drawings and more p sides of the tank where they are subjected inticularly to Fig. 1, the pressure vessel is shown directly to heat from the fire. These thermoas a horizontally disposed cylindrical steel tank couples operate galvanometers, which in turn 20 having a temperature-controlled relief valve operate suitable relays which operate a solenoidll. This relief valve may also be responsive to operated relief valve. Provision may be made for tank pressure. Surrounding the tank 20 on sides the relief valve to open at a predetermined higher and ends are the hot junctions IQ of the thermotemperature but not to re-close until the temcouples. These hot junctions l9 are associated perature falls to a prdetermined lower value. with a cold junction [8 which may be located Provision may also be made for preventing autoabove the tank 20 in a position unlikely to be afmatic reclosing of the relief valve and to place fected by accidental fire. The control instrureclosing under -manual control. Instead of ments discussed below will also be located in a thermocouples, other temperature responsive spot protected from fire. elements may be used, as for example, bimetallic It will be understood that the diiferent metals thermostats. making up the thermocouples extend all the way The invention also consists in certain new and from the hot junctions IE to the cold junction original features and combinations hereinafter l8. One metal may be iron, for example, and is set forth and claimed. indicated by 34. The other metal may be con- Although the novel features which are bestantan and is indicated by 35. Thus the wire 34 lieved to be characteristic of this invention will be comprises iron all the way from terminal A to the particularly pointed out in the claims appended several hot junctions l9 and the wire 35 comhereto, the invention itself, as to its objects and prises constantan all the way from terminal B advantages, and the manner in which it may be to the several hot junctions l 9. The metal of the carried out, maybebetter understood by referring wires 31 connecting cold junction IS with the to the following description taken in connection rest of the circuit may be conventional copper. with the accompanying drawings forming a part The iron and constantan wires 34,35, as well as hereof, in which: the other wiring discussed below, may be en- Fig. 1 illustrates diagrammatically a circuit closed in suitable protecting conduits. The hot arrangement in which a temperature responsive junctions l9 are shown as connected in parallel. relief valve iscontrolled bya plurality of thermo- They may alSO be connected in series. The couples; thermocouple hot junctions and the connecting Fig 2 ill t t diagrammatically a i it; wires may be placed on the inside of the tank, arrangement in which the relief valve is coninstead of on the outside. trolled by one or more bimetallic thermostats; For responding to the electrical potential and created by the fire heating any one or more of the Fig. 3 illustrates diagrammatically a circuit hot junctions 19, two galvanometers H and I2 are shown. The low temperature galvanometer l i may respond to a predetermined low temperature difference, say 400 F. between any one hot junction l9 and cold junction [8. The high temperature" galvanometer l2 may be actuated when the temperature difference between any one hot junction and the cold junction is, say, 600 F. These galvanometers are of similar construction having the usual movable coils 22 and 23 operating between magnets having north and south poles, N and S. Movementof the coils 22 and 23 closes the contacts 24 and 25 as will be understood.

The galvanometers ll, l2 control a solenoid switch of conventional construction comprising a solenoid winding 26, main contacts 21 and holding contacts 28. A locking relay [3 is also provided having a winding 29 and contacts 30. Low voltage battery 14 is also provided. Conventional high voltage power source is denoted by IR, manual switch by H).

The relief valve ll includes a solenoid winding 3| operating against spring 40 to raise valve disc 33 seating in the valve casing 32. The valve 33 opens either in response to pressure inside the tank or to current passing through the solenoid winding 3|. In either case the gas is vented to a safe point of disposal such as a stack (not shown).

Solenoid 31 may be so designed that a small predetermined tank pressure, say five to ten pounds per square inch, gauge, will open valve I! while the solenoid 3| is actuated, but valve I! will be closed by spring 40 should the tank pressure fall below this figure, even though solenoid 3| is still actuated. Thus the tank pressure may be prevented from falling to an unsafe low pressure as a result of venting, and the tank may be prevented from drawing in air upon cooling.

The several parts are wired as indicated. The galvanometer coils 22 and 23 are connected in parallel to the cold junction l8 by wires 31. The battery I is connected in circuit with the high temperature galvanometer contacts 24 and with the winding 29 of the locking relay. The battery 14 is also in circuit with the contacts 25 of the low temperature galvanometer, the holding contacts 28, and the winding 29 of the locking relay. It will be noted that the winding 29 is thus under control of two parallel circuits connected at the points 38 and 39.

The source of electricity l6, which may be ordinary commercial A. C. or D. C. power, is connected in series with the solenoid winding 26 of switch l5 and the contacts 30 of the locking relay l3. Power source I6 is also connected in series with the solenoid winding 3| of the relief valve l1 and the main contacts 21 of the solenoid switch l5. Manual switch I0 is connected across low temperature galvanometer contacts 25.

The manual switch I0, when closed, prevents reclosing of the relief valve I! after opening due to fire except when the relation between solenoid strength and valve spring is such as to cause valve 33 to seat when the small predetermined tank pressure of five to ten pounds per square inch, gauge, is reached. as above explained.

Operation of the circuit will first be explained with the manual switch l0 open.

When fire around gas tank 20 causes the differential temperature between any one hot junction l9 and cold junction [8 to exceed the set 400 F., low temperature galvanometer contacts 25 close but nothing happens because holding contacts 28 of solenoid switch are open. When Ill the said temperature differential reaches the set 600 F., high temperature galvanometer contacts 24 close completing the circuit through battery l4 and winding 29 of the locking relay, closing looking relay contacts 30. This completes the circuit from power source l6 through winding 26 of the solenoid switch operating it to close main contacts 21 and auxiliary contacts 28.

Main contacts 21 close the circuit from power source l6 through the winding 3| of relief valve ll opening disc 33 and venting the tank gases to stack. Auxiliary contacts 28 lock solenoid switch l5 closed under control of contacts 25 of the low temperature galvanometer.

When the fire is brought under control and the temperature decreases to the 600 F. differential, high temperature galvanometer contacts 24 open, but nothing happens because solenoid switch [5 is held closed by low temperature galvanometer contacts 25. When the temperature differential falls to 400 F., contacts 25 open which releases locking relay l3 whose contacts 30 open and release solenoid switch [5. Opening of solenoid switch contacts 21 opens the circuit through the relief valve winding 3|, permitting spring 40 plus gravity to close relief valve ll.

It will b noted that the manual switch i0 is in parallel with the contacts of the low temperature galvanometer ll. Thus, when manual switch [0 is closed, solenoid 3| remains actuated even though both contacts 2| and 25 are open. Relief valve ll will then remain open until tank pressure has fallen to the predetermined low figure of five to ten pounds per square inch, gauge, when spring 40 will overcome the solenoid and close valve H. As explained hereinbefore, the closing of valve H at such a predetermined low superatmospheric pressure will prevent tank 20 from drawing in air upon further cooling.

The E. M. F. created by a temperature difference between hot junctions I9 and cold junction l8 will depend upon how many of the hot junc tions are heated, and how hot each becomes. The hot junctions are assumed to be at the temperature of the adjacent tank wall, to which they are attached.

When the tank is exposed to a fire, the cooling effect of the boiling liquid will tend to keep the tank at a safe temperature even though the internal pressure may be high enough to cause relief valve l! to open in response to pressure alone. The danger which this invention avoids results when the portion of the tank exposed to the fire is no longer cooled by boiling liquid. as

' when all or nearly all the liquid has vaporized.

Tank pressure may then fall, as a result of venting, to a value below the closing pressure of the relief valve, in which case the latter would close. However, if any portion of the tank is at an unsafe temperature, i. e., if any one of the hot junctions is above the predetermined opening temperature, the solenoid will be actuated and the relief valve opened.

Referring now to Fig. 2, here the source of commercial A. C. or D. C. power is indicated by 50, this source feeding a transformer 5|. Current from the secondary 59 of the transformer operates a solenoid switch 53 which is under control of a plurality of bimetallic thermostats, one of which is indicated by 52. The winding 3la corresponds to winding 3| of relief valve ll in Fig. 1 and is for the purpose of operating a corresponding relief valve. The plurality of thermostats 52 will be located at strategic points around the tank to be protected where they will be affected by fire. A manual switch 55 is also provided.

The thermostat 52 comprises a bimetallic strip 54 so mounted that the end carrying contacts 56, 51 moves in the directions indicated when subject to temperature change. The contacts 56 and 51 have different spacings so that low temperature" contact 51 may close when a temperature of say 400 F. is reached and high temperature contact 56 may close when a temperature of say 600 F. is reached.

The transformer 5| may be a step-down transformer having a primary 58 and a secondary 59. The solenoid switch 53 has solenoid winding 49, main contacts 60 and holding contacts 6|.

The apparatus is wired as indicated, the power source 50 being connected to relief valve solenoid 3la through main contacts 60. The solenoid switch winding 49 is under control of a low temperature circuit including low temperature contacts 51, holding contacts 6|, winding 53, secondary 59, lead 63 connected to the bimetallic,

strip 54 to complete the circuit. The solenoid switch winding 49 is also under control of a high temperature circuit which includes high temperature contacts 56, winding 53, secondary 59, lead 63 and bimetallic strip 54. It will thus be noted that the solenoid switch winding 49 is under control of two parallel circuits connected together at the points 62 and thermostat 52. The manual switch 55 bridges low temperature contacts 51, as indicated.

Although for simplicity only one thermostat 52 is shown, there may be a plurality of thermostats distributed around the tank as are the hot junctions IS in Fig. l. The additional thermostats 52 will be connected in parallel at the points C, D and E. Thermostats other than bimetallic may also be used.

The operation of this circuit is as follows, as-

suming, first, that manual switch 55 is open. When a conflagration occurs, one of the thermostats 52 heats up closing low temperature contacts 51 at say 400 F. but nothing will happen since holding contacts 6| are open. When the temperature reaches, say, 600 F., high temperature contacts 56 close completing the circuit through solenoid winding 49 and closing the solenoid switch 53. This closes main contacts 60 which opens the relief valve having winding 31a. The holding contacts 6| also being closed, solenoid switch 53 is now locked closed under control of low temperature contacts 51. Thus, when the fire is extinguished and the temperature is reduced to 600 F., the opening of high temperature contacts 56 will not open the solenoid switch 53; this switch will not open until the temperature falls to 400 F. at which the low temperature contacts 51 are set to open. When contacts 51 open, the solenoid switch 53 releases which in turn closes the relief valve whose winding is 3la.

As in Fig. 1, if desired, the manual switch 55 may be kept closed in which case the solenoid switch 53 will not open when low temperature contacts 51 open but will stay closed, thus preventing the relief valve corresponding to winding 31a from reclosing until switch 55 is manually opened, or until tank pressure has fallen to the predetermined value of five'to ten pounds per square inch, gauge.

In Fig. 3 is shown diagrammatically a circuit identical with that of Fig. 2 except that the thermostats 52 are replaced with a plurality of millivoltmeters, one of which is indicated by H, actuated by thermocouples having their hot junctions, one of which is indicated by 61, disposed at suitable locations on the surface of tank 20. Millivoltmeters ll may be placed in a safe location as on the top of tank 20, and each may be connected to its respective thermocouple hot junction 61 by thermocouple wires TI. These wires, or suitable extension leads, may terminate in millivoltmeter coil 68 in a conventional manner. Millivoltmeter pointer 14 is provided with a contact 13 at its outer end which is connected to point C by lead 64. Stationary contacts 69 and 10 are connected to points D and E, respectively, by leads 65 and 66. Stops 15 and 16 are provided to prevent excessive travel of pointer I The operation of Fig. 3 is similar to that of Fig. 2. The E. M. F. set up as a result of a confiagration affecting any one of the hot junctions 61 will cause the millivoltmeter pointer 14 to move toward contact 10. Millivoltmeter H may be so designed that contact piece I3 touches contact 10 when the temperature of the tank wall (as measured by thermocouple hot junction 61) has reached a predetermined low temperature of, say, 400 F. This completes a portion of the circuit across the points C and E, through leads 64 and 66, and contacts 10 and 13, but nothing happens because contacts 61 are open. If the temperature at the hot junction 6! continues to rise until a dangerously high temperature of, say, 600 F. is reached, pointer 14 continues to move to the right until contact is made between movable contact 13 and both stationary contacts 69 and 10. Contact between elements 13 and 69 completes the circuit con-.

taining secondary coil 59 of transformer 5|, solenoid switch 53, leads 64 and 65. Solenoid switch ,53 is thus actuated, closing contacts 60 and 6|. Closing of contacts 60 actuates solenoid 3m to open the relief valve. Stop I6 prevents further movement of pointer 14 to the right, regardless of the temperature ultimately reached at the hot junctions 61.

When the fire is brought under control and the temperature at the hot junction 61 falls below 600 F. the contact between 69 and I3 is broken. However, so long as there is contact between 13 and 10, solenoid switch 53 will remain closed and the relief valve open. Upon further cooling to below 400 F. the contact between 10 and I3 is broken and (unless manual switch 55 is closed) solenoid switch 53 is de-energized and opens. This breaks contact at points 60, de-energizes solenoid 3la, and permits spring 40 to close valve 33.

From each of the above forms of the invention it will be seen that the relief valve opens when an unsafe temperature is reached. Thus the relief valve will open at a less pressure when the tank is subjected to the intense heat of fire because the steel walls of the tank weakened by intense heat will rupture at less pressure. Without the protection of this invention a tank with conventional pressure relief valve has been known to rupture under the force of ordinarily safe pressure acting upon heat-weakened steel.

The setting of the reclosing temperature less than the opening temperature provides a margin of safety by insuring the return to safe operating temperature, when the steel has recovered some of its strength, before allowing pressure to build up again in the tank. At the same time reclosing of the relief valve saves any liquid or gas remaining in the tank when'the fire is brought under control. However, in the event conditions make it inadvisable to re-close automatically the safety valve after a fire, the manual switch may be kept closed, thus keeping the safety valve open until tank pressure has dropped to a safe figure, say, five to ten pounds per square inch, gauge. Spring 40 will then overcome solenoid 3| to automaticallyclose the valve and prevent the possibility of air being drawn into the tank upon further cooling.

While certain novel features of the invention have been disclosed herein, and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is: r

1. In a safety system for storing high presture fluid, a storage vessel, a relief valve on said vessel, a temperature responsive device adjacent said vessel and subject to confiagration, an electric motor for opening said relief valve, and electric means governed by said temperature responsive device for operating said motor to open said relief valve, said relief valve having means responsive to internal pressure for opening said valve.

2. In a safety system for storing high pressure fluid, a storage vessel, a relief valve on said vessel, a temperature responsive device adjacent said vessel and subject to conflagration, and means governed by said temperature responsive device for opening said relief valve at a predetermined higher temperature and closing said relief valve at a predetermined lower temperature.

3. In a safety system for storing high pressure material, a storage vessel, a solenoid relief valve on said vessel, a temperature responsive device adjacent said vessel and subject to confiagration temperature, a solenoid switch having main contacts and holding contacts, said temperature responsive device having low temperature contacts and high temperature contacts, said solenoid switch being under control by said high temperature contacts and under series control by said low temperatur contacts and said holding contacts; a source of power. said main contacts being in series with said source of power and the winding of said relief valve.

4. In a safety system for storing high pressure petroleum gas, a storage vessel, a solenoid relief valve on said vessel, a plurality of temperature responsive devices around said vessel and subject to conflagration temperature, a solenoid switch having main contacts and holding contacts, said temperature responsive devices having low teml perature contacts and high temperature contacts,

said solenoid switch being under control by said high temperature contacts and under series control by said low temperature contacts and said holding contacts; a source of power, said main contacts being in series with said source of power and the winding of said relief valve, and a manual swich bridged across said low temperature contacts. a

5. In a safety system for storing high pressure fluid, a storage vessel, a solenoid relief valve on said vessel, a thermocouple having its hot junction adjacent said vessel and subject to conflagrations, a low temperature galvanometer and a high temperature galvanometer operated su're petroleum gas, a storage vessel, a solenoid relief valve on said vessel, a plurality of thermocouples having their hot junctions around said vessel and subject to conflagration, a low temperature galvanometer and a high temperature galvanometer operated by said thermocouples, a solenoid switch having main contacts and holding contacts, a locking relay, a source of low voltage, a source of high voltage, a circuit including serially said low voltage source, with winding of said locking relay, said holding contacts and said low temperature contacts; said high temperature contacts being connected across that part of said circuit including said low temperature contacts and holding contacts; a manually operated switch bridged across said low temperature contacts; a second circuit including serially the winding of said solenoid switch, said looking relay contacts and said high voltage source; and an additional circuit including serially the winding of said solenoid relief valve, said main contacts and said high voltage source.

'7. In a safety system for storing high pressure fluid, a storage vessel, a solenoid relief valve on said vessel, a thermostat adjacent said vessel at a point subject to conflagratiomsaid thermostat having low temperature contacts and high temperature contacts, a source of electric power, a transformer fed by said source, a solenoid switch having main contacts and holding contacts, a circuit including serially the Winding of said reliefvalve, said source of power and said main contacts; a second circuit including serially the winding of said solenoid switch, the secondary of said transformer and said high temperature contacts; a third circuit bridged across said high temperature contacts and including serially said v tacts, a source of electric power, a transformer by said thermocouple, a solenoid switch having I fed by said source, a solenoid switch having main contacts and holding contacts, a circuit including serially the windingof said relief valve, said source of power and said main contacts; a second circuit including serially the winding of said solenoid switch, the secondary of said transformer and said high temperature contacts; a third circuit bridged across said high temperature contacts-and including serially said low temperature contacts and said holding contacts; and a manually operated switch bridged across said low temperature contacts.

9. In a safety system for storing high pressure fluid, a storage vessel, a solenoid relief valve on said vessel, a thermocouple having its hot junction adjacent said vessel at a point subject to conflagration, a millivoltmeter having a coil connected to said hot junction and having low temperature contacts and high temperature contacts engageable by movement of said coil, a source of electric power, a transformer fed by said source, a solenoid switch having main contacts and holding contacts, a circuit including serially the winding of said relief valve, said source of power and said main contacts; a second circuit including serially the winding of said solenoid switch, the secondary of said transformer and said high temperature contacts; a third circuit bridged across said high temperature contacts and including serially said low temperature contacts and said holding contacts.

10. In a safety system for storing high pressure petroleum gas, a storage vessel, a solenoid relief valve on said vessel, a plurality of thermocouples having their hot junctions around said vessel at points subject to oonflagration, a millivoltmeter for each thermocouple having a coil connected to said hot junction and having low temperature contacts and high temperature contacts engageable by movement of said coil, a source of lectric power, a transformer fedby said source, a solenoid switch having main contacts and holding contacts, a circuit including serially thewinding of said relief valve, said source of. power and said main contacts; a second circuit including serially the winding of said solenoid switch,--the secondary of said transformer and said high temperature contacts; a third circuit bridged across said high temperature contacts and including serially said low temperature contacts and said holding contacts; and a manually operated switch bridged across said low temperature contacts.

11. In a safety system for storing high pressure fluid, a storage vessel, a relief valve on said vessel and operable by pressure of fluid within said vessel, restoring means operating to close said valve, a temperature responsive device adjacent said vessel and subject to conflagration, opening means governed by said temperature responsive device for opening said relief 7 valve against the force exerted by said restoring means, said opening means and said restoring means being so related that at a predetermined fluid pressure within said storage vessel said restoring means operates to close said relief valve regardless of energization of said opening means.

12. In a safety system for storing high pressure liquefiable gas, a storage vessel having walls of such extended area that portions of them may be heated by a local conflagration to such unsafe temperature as to weaken them while other portions remain at safe temperatures, said storage vessel being thereby subject to unsafe conditions under which the pressure of the stored gas may be too high for the strength of said weakened wall portions, safety means for restor- 10 ing said vessel to safe condition under which the pressure of the stored gas is not too high for the strength of the wall of the vessel, said safety means comprising a pressure relief valve on said vessel, said pressure relief valve being operable in response to pressure inside said vessel, a plurality of temperature-responsive devices distributed along said walls so as to be individually subjected to said local conflagration, and means v governed by the response to said local conflagration of any one or more of said temperatureresponsive devices, regardless of the temperature of the other temperature-responsive devices, for opening said pressure relief valve,

13. In a safety system for storing high pressure liqueflable gas, a storage vessel having walls of such extended area that portions of them may be heated by a local conflagration to such unsafe temperature as to weaken them while other portions remain at safe temperatures, said storage vessel being thereby subject to unsafe pressuretcmperature relationship under which the pressure of the stored gas is too high for the strength of "said weakened wall portions, safety means for restoring to said vessel a safe pressure-temperature relationship under which the pressure of the stored gas is'not too high for the strength of the wall of the vessel, said safety means comprising a. relief valve "on said vessel, a plurality of temperature-responsive devices distributed along said walls so as to be individually subjected to said local conflagration, means governed by the response to said local conflagration of any one or more of said temperature-responsive devices, re-

P gardless of the temperature of the other temperature-responsive devices, for opening said relief valve, and means governed by return of safe pressure-temperature relationship for reclosing said relief valve while substantial, but safe, pressure remains in the vessel.

GEORGE R. BENZ.

ELMER O. MATTOCKS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

